Technologies for uniformly irradiating a predetermined plane with laser light emitted from a light source such as a semiconductor laser have conventionally been proposed. For example, in a light irradiation apparatus in which laser light incident from a light source part is divided by a plurality of lenses in a cylindrical lens array and irradiation regions of the light from the plurality of lenses are superimposed on one another in an irradiation plane by another lens, an optical path length difference generation part is provided between the light source part and the cylindrical lens array. The optical path length difference generation part includes a plurality of transparent parts that produce a difference in optical path length between each other, the difference being longer than the coherence distance (coherence length) of the laser light, and light that has passed through the plurality of transparent parts respectively enters the plurality of cylindrical lenses. This prevents interference fringes from appearing and achieves uniformity of the intensity distribution of the light irradiated onto the irradiation plane (as examples of such an apparatus, see Japanese Patent Application Laid-Open Nos. 61-169815, 2004-12757, and 2006-49656, for example).
Incidentally, in a drawing apparatus in which a spatial light modulator is disposed in the irradiation plane in the above-described light irradiation apparatus and spatially modulated light is irradiated onto an object to draw a pattern, a light irradiation apparatus capable of irradiating the irradiation plane with high-intensity light having a uniform intensity distribution is required in order to increase the speed of pattern drawing.